21004 has 12 divisors (see below), whose sum is σ = 37800. Its totient is φ = 10208.

The previous prime is 21001. The next prime is 21011. The reversal of 21004 is 40012.

It is not an unprimeable number, because it can be changed into a prime (21001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 192 + ... + 280.

It is an arithmetic number, because the mean of its divisors is an integer number (3150).

2²¹⁰⁰⁴ is an apocalyptic number.

It is an amenable number.

21004 is a deficient number, since it is larger than the sum of its proper divisors (16796).

21004 is a wasteful number, since it uses less digits than its factorization.

21004 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 152 (or 150 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 7.

The square root of 21004 is about 144.9275681159. The cubic root of 21004 is about 27.5909933505.

Adding to 21004 its reverse (40012), we get a palindrome (61016).

The spelling of 21004 in words is "twenty-one thousand, four", and thus it is an iban number.